The turquoise color of Lower Grinnell Lake, in the foreground, is caused by "glacial milk," suspended calcium carbonate (limestone) in the meltwater runoff of Grinnell and Salamander Glaciers. The glaciers move slowly downhill and grind their limestone bed into fine particles, which remain in suspension and flow with the meltwater in the waterfalls. Lake Josephine, in the distance, is a more typical blue color because it is fed by other mountain streams as well. This valley, like others in Glacier National Park, was carved into a U-shape by the huge contintental glaciers of the Pleistocene epoch.
© Gregory G. and Mary Beth Dimijian